Studies of speech motor learning: Practice effects on movement displacement velocity and duration were studied while learning a novel speech task and an oral movement task in normal adults and patients with cerebellar degeneration. Both groups significantly reduced jaw closing displacement and speed of movement with practice, similar to effects of practice in other fine motor skills such as handwriting and typewriting. This suggests that becoming more skilled for previously learned speech movements involves moving less, perhaps to increase movement control, efficiency and/or accuracy. Practice effects for the oral movement sequence task were more like those reported for limb movements. Only the group of normal control subjects demonstrated a pattern of increased movement speed and consistency on the oral movement sequence task with practice. Therefore, cerebellar patients were impaired in learning novel, non-speech oral movements. The findings suggest that cerebellar pathology does not affect practice of previously learned movements but does impair learning of novel movements. Studies of Speech Planning: The study of speech planning contrasts speech initiation and execution when the speaker must either switch to a new phrase or restart the same item following an unanticipated interruption. Normal speakers were faster and more fluent when a new and different phrase was required following interruption demonstrating that during phonation on line planning for a new and different speech item is possible in normal speakers. Examination of a Familial Form of Cluttering: Abnormalities present only in affected cluttering family members were phonemic retrieval and repetition, melodic imitation, rhyming, singing and writing. The disorder is one of speech sound representation affecting speaking and writing and melodic representation affecting singing. The pedigree contained a higher proportion of affected males suggesting an autosomal sex modified trait.